The requirements for increasingly high areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr) , magnetic remanance (Mr) , Mr times thickness (Mrt), coercivity squareness (S*) , medium noise, i.e., signal-to-noise ratio (SNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the coercivity of the magnetic recording medium. However, this objective can only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise is a dominant factor restricting increased recording density of high density magnetic hard disk drives. Medium noise in thin films is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
A conventional longitudinal recording disk medium is depicted in FIG. 1 and comprises a substrate 10, typically an aluminum (Al) or an (Al)-alloy, such as an Al-magnesium (AlMg) alloy, plated with a layer of amorphous nickel-phosphorous (NiP). Alternative substrates include glass, ceramic, silicon, plastics, glass-ceramic materials, as well as graphite. There are typically sequentially sputter deposited on each side of substrate 10 an adhesion enhancement layer 11, 11', e.g., chromium (Cr) or a Cr alloy, a seedlayer 12, 12', such as NiP, an underlayer 13, 13', such as Cr or a Cr alloy, a magnetic layer 14, 14', such as a cobalt (Co)-based alloy, and a protective overcoat 15, 15', such as a carbon-containing overcoat. Typically, although not shown for illustrative convenience, a lubricant topcoat is applied on the protective overcoat 15, 15'.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is recognized that underlayers having a fine grain structure are highly desirable, particular for growing fine grains of hexagonal close packed (HCP) Co alloys deposited thereon.
As the requirements for high areal recording density escalate it becomes increasingly more important to provide high recording signals and low medium noise. Consequently, it is necessary to develop thin film structure fabrication techniques which favorably affect the microstructure, surface orientation and grain structure of the deposited films. Previously, efforts have been made to obtain suitable thin film media with advantageous magnetic performance and recording performance by varying the materials employed for the seedlayer, underlayer or buffer layer for longitudinal magnetic recording media. The epitaxial growth of a magnetic material on such layers imparts a certain crystallographic structure which results in certain magnetic properties.
Different sputtering conditions also impact the resulting magnetic proprieties, including substrate heating, varying the film thickness, and altering the re-sputtering gas and pressure. Such sputtering conditions alter the energies of the sputtered atoms and, hence, alter the growth mechanism of the films, as by thermal diffusion, crystallization and lattice matching or expansion. A substrate bias of about 100 to about 250 volts has been applied during thin film deposition. The application of a substrate bias would also increase sputtering on the grown films, further altering the surface morphology as well as crystallographic structure, thereby influencing the magnetic performance of the resulting media.
There exists a continuing need for simplified methodology enabling the fabrication of high areal recording density magnetic recording media exhibiting a high Hr, high S* and high SNR.